For illumination purposes, a light source should advantageously generate a light field having an intensity distribution that decays continuously and monotonically in radial direction, or that is homogeneous over a certain radius.
However, an LED light source, in particular an LED light source comprising a large LED or an array of LEDs, is not a point light source, and the photons emitted by its active surface are divergent and have poor spatial correlation. Hence, it is difficult to process the light field emitted by an LED light source in order to efficiently obtain a light field suited for illumination purposes.
US 2006/0045501 describes an LED light source that generates a divergent light field. This light field is processed by a first optical element structured to generate a collimated light field. The collimated light field is sent onto a second optical element having variable focus. The second optical element generates a light field of variable divergence.